Check valve



FIG. 1 is a side view of a check valve showing my new design; the design being radially symmetrical, all side views are the same;

FIG. 2 is a lower perspective view thereof;

FIG. 3 is an upper perspective view thereof;

FIG. 4 is a top view thereof; and,

FIG. 5 is a bottom view. 

CLAIM The ornamental design for a check valve, as shown and described. 